The data storage industry is always striving for innovations to improve areal density of hard disk drives. Improvements can be achieved through changes to the design of the head, the disk, or a combination of the two (e.g., perpendicular head recording).
FIGS. 1A and 1B show front and side views respectively of an exemplary prior art write head 100 of a hard disk drive. Write head 100 comprises an upper pole 110, also known as a “P2” pole, a lower pole 120, also known as a “P1 pedestal,” or “P1P”, and a write gap 130 disposed between the P1P and P2. Write head 100 further comprises a plurality of coils 140.
FIG. 2 shows the composition of an exemplary prior art write gap 130. Typically, write gap 130 comprises one or more layers of a magnetically inert material disposed between the P2 (110) and P1P (120) poles. For example, in FIG. 2, a first inert layer 210 is a layer of Rhodium which is approximately 900 angstroms (900 A) thick disposed above a second inert layer 220 of Tantalum which is approximately 100 angstroms (100 A) thick. In other prior art implementations, write gap 130 may comprise a layer of alumina, which is disposed between P2 (110) and P1P (120).
Returning now to FIGS. 1A and 1B, in operation, the surfaces of P2 (110) and P1P (120) adjacent to the gap (130) are saturated to generate a magnetic field, which magnetizes a recording medium (e.g., a magnetic disk). It is typically desired to maximize the magnetic flux density in the write gap to improve writing efficiency. However, when saturating write gap 130, additional magnetic fields are created in regions 150 and/or 160 of the P1P (120). These additional stray magnetic fields can be problematic because they are associated with a weak, unreadable signal which cannot reliably store magnetic charges on the recording medium. However, the stray fields can interfere with the storage of data on adjacent recording tracks of the recording medium by partially overwriting, or even erasing, the data on the adjacent tracks.
This is shown more clearly in FIG. 3, which shows the orientation of an exemplary prior art write head 100 relative to recording tracks of a recording medium. As shown in FIG. 3, write head 100 is disposed at an angle relative to direction of recording tracks 310, 320, and 330 and, when in operation, recording tracks move in the direction indicated by arrow 340. As shown in FIG. 3, each of the recording tracks comprises a write track (e.g., 311, 321, and 331 respectively) as well as erase bands (e.g., 310a, 310b, 320a, 320b, 330a and 330b respectively) which are adjacent to their respective write tracks.
As described above, when the surfaces of P2 (110) and P1P (120) are saturated, regions 150 and/or 160 may also emit a magnetic field. As shown in FIG. 3, region 150 overlies erase band 310b and generates a magnetic field, which magnetizes some regions in erase band 310b. The magnetic field generated in region 160 actually overlies write band 311. However, it is overwritten by the stronger magnetic field generated by write gap 130 as the recording track moves beneath write head 100.
Because the erase bands can interfere with data storage in adjacent recording tracks, a certain amount of offset (e.g., 350) between recording tracks, also referred to as “pitch” is typically provided. However, the extra space required to provide this offset reduces the density of data, which can be stored on the magnetic disk.